Various methods have been previously known for bonding materials of the same kind, such as metals to metals or ceramics to ceramics, or materials of different kinds, such as metals to ceramics.
For instance, fusion welding methods for bonding metals to metals include electric welding, gas welding, friction welding, diffusion welding, etc. Further, conventional methods include brazing treatment or adhesion with organic adhesives, in which substrates are not melted.
Also, known methods include adhesion with organic adhesives or heat-resistant metallic adhesives for bonding ceramics to ceramics, as disclosed in Japanese patent application (OPI) No. 58870/86. (The term "OPI" as used herein means an "unexamined published Japanese patent application.")
Apart from bonding materials of the same kind, known adhesion methods include organic adhesives, active metallic adhesives, shrinkage fitting methods, solid phase-reacting adhesives, etc. for bonding materials of different kinds such as metals to ceramics. Further a heat-resistant metallic bond can be produced by metallizing a ceramic substrate with Mo or W, plating it with a nickel plate, and then soldering it to a metal substrate. Recently, a bonding technique has been developed utilizing a chemical reaction in which an inorganic oxide series adhesive is used for formation of a hydrate compound.
However, all of the above-mentioned bonding methods, except fusion welding which is an inherent method for bonding metal to metal, have the defects that the bonds are weak under heat and the adhesion strength is not sufficient.
On the other hand, other bonding techniques have been proposed by means of evaporation plating, sputtering, metal spraying, etc. or by the use of foil-shaped insert materials. These are, however, hardly practical and commercially unsatisfactory, since not only is the adhesion strength inadequate, but also the field of application is limited.
In particular, for bonding combinations including a ceramic material, such as a ceramic to a ceramic or a ceramic to a metal, for example, where a substrate of SiC or graphite is bonded with another substrate of a ceramic material (such as SiC or alumina) or a metal, there is no practical method at present except the general use of organic adhesives. The use of organic adhesives is, however, not practical, since the environment for their use is restricted to about 150.degree. C. or below because of the characteristics of the SiC or graphite substrate and of organic adhesives. Further, the bonded parts have poor weather-resistance and insufficient strength.
The present inventors have earnestly studied the improvement of heat resistance in metallic material adhesive, and methods for increasing especially the adhesion strength of metallic material adhesives, and, as a result, have found that the mere regulation of the chemical components of the adhesive, such as in conventional metallic brazing materials (e.g., Japanese patent publication No. 10235/86), results in the materials having limited use, and further is not sufficient for satisfying the requirements for improved heat-resistance and adhesion strength.